Process of making indigo.



UN TE' .s'ra'irns PATENT oFFIoE.

ARNOLD RAHTJEN AND OAR-L STEPHAN, OF HAMBURG, GERMANY; SAID STEPI-IAN ASSIGNOR TO SAID RAHTJEN.

PROCESS OF MAKING INDIGO.

Specification of Letters Patent.

Patented April 16, 1907 Application filed January 29, 1906. Serial No. 298.556.

vented certain Improvements in Processes of Making Indigo; and We do hereby declare the nature of our invention to be as follows.

We have discovered that artificial indigo is obtained when a-isatin anilid, dissolved or sus ended in a suitable solution, is treated wit hydrogen sulfid, (H 8) Our invention consists in a process of making indigo in which the discovery is utilized.

In the (practice of our process the a-isatin anilid is resolved or suspended in any suitable alkaline or neutral liquid, ethyl alcoholbeing well adapted for this purpose. Hydrogen sulfid is then added. Indigo is not in all cases immediately produced upon the addition of the hydrogen sulfid. Sometimes in termediate products result which may be isolated, although that is not necessary for the successful practice of our process. These intermediate roducts change into indigo so easily that t 1e application of heat results in the immediate production of indigo. At a lower temperature the intermediate products, dissolved or suspended in suitable liquids which contain an excess of hydrogen sulfid, change into indi o gradually; but the process can be carried out by adding reagents, as hereinafter illustrated. The anilid split off is easily regained and the separated sulfur is separated from the indigo in the usual manner.

The following .examples illustrate various methods in which my invention can be successfully carried out.

Example 1 Ten parts, by weight, of a-isatin anilid are dissolved in thirty or forty parts of alcohol. Then introduce hydrogen sulfid (H 8) at ordinary temperature until the liquid is almost colorless. Then add water and precipitate the indigo by blowing air into the resulting mixture.

Example 2: Proceed as under Example 1,

but instead of blowing in air increase the temperature gradually up to to 80 Celsius, whereupon the indigo separates out.

-Example.3: Treat a solution of oz-isatin anilid as under Example 1,- but instead of blowing in air add nitric, sulfuric, or any other suitable acid, whereupon the indigo separates out.

. Example 4: Treat the solution ofd-isatinanilid as under Example 1 with hydrogen sulfid (H S) and add traces of ammonia, soda, andsuch like agents, whereupon indigo separates out.

Example 5: Into a boiling solutionof aisatinanilid in pure or diluted alcohol or in aceton, benzol, or like suitable liquids hydro gen sulfid (H S) is introduced until the liquid is almost colorless, whereupon crystallizedindigo separates out.

Example 6: Suspend a-isatin anilid in water in which traces of alkali are preferably dissolved, introduce hydrogen sulfid and heat the liquid from 25 to 100Celsius. Indigo inthe form of a very fine powder is thus produced.

Having thus described an invention, what we claim, and desire to secure by Letters Patent, is

1. In a process of producing indigo, reacting upon ur-isatin anilid with hydrogen sulfid.

2. In a process of producing indigo, pa sing hydrogen sulfid into a liquid containinga-isatin anilid.

3. In a process of producing indi 0, passing hydrogen sulfid into liquid ho ding aisatin anilid in suspension.

4. In a process of producing indigo, passing hydrogen sulfid into alcohol containing wisatin anilid. l

5. In a process of producing indigo, reacting upon a-isatin anilid with hydrogen sulfid and subjecting the intermediate products thus formed to heat.

6. In aprocess of producing indigo, reacting upon a-isatin anilid with hydrogen sulfid and heating the resulting material until indigo is precipitated. I

7. In a process of producing indigo, reacting upon a-isatin anilid with hydrogen sulfid I 25 to 100 C. and separating the resulting in the presence of a liquid and heating the precipitate from the remaining liquid.

' Dated this 15th day of January, 1906.

ARNOLD RAHTJE; CARL S'l-EPHAN.

resulting materlal to a temperature of from 25 to 100 Celsius.

8. In a process of producing indigo, first reacting upon a-isatin anilid, suspended in alcohol, with hydrogen 'sulfid, heating the resulting'niaterial to a temperature of from 1 Witnesses:

ERNEST H. L MUMMENHOFF, IDA CHRIST. HAFERMANN. 

